The present invention relates generally to the preparation of organoclays via ion exchange with a quaternary ammonium halide. More specifically, the present invention relates to preparing organically modified smectites having improved rheological properties for use in invert emulsion drilling fluids, greases, paints and the like by a dry process in which pulverized smectite is added to a solution of methyl benzyl dialkyl ammonium halide salt to produce via ion exchange the improved organoclay.
Smectites are clay minerals, including montmorillonite, saponite, beidellite, and hectorite, which are characterized by their swelling properties and high cation-exchange capacities. Bentonite, a rock term in which the main mineral is smectite, is formed as a result of the alteration of volcanic ash. Smectites, and bentonites, whose exchangeable cations are mainly sodium, are respectively known to those skilled in the art as sodium smectite and sodium bentonite, and those whose exchangeable cations are mainly calcium and/or magnesium are respectively known to those skilled in the art as alkaline earth smectites and alkaline earth bentonite. The cation exchange capacities of pure smectites generally range between 75 milliequivalents per 100 grams clay to 110 milliequivalents per 100 grams clay.
It is well known to those skilled in the art that the rheological properties of drilling muds, greases, paints and the like can be improved by the incorporation of organically modified clays. Typically, organoclays for these purposes are formed by the so-called "wet" process, as, heretofore, the rheological properties of organoclays produced via the so-called "dry" process have been significantly poorer than those exhibited by "wet" processed organoclays.
In the typical "wet" process for preparing organoclays, the crude clay is water fractionated in a low solids slurry, typically in the range of 6 to 8 percent, to remove all particles greater than about 2 microns. The greater than 2 microns fraction is discarded, while the remaining fraction, which consists essentially of only the montmorillonite fraction of the crude clay, is then reacted with an amine, such as a quaternary ammonium halide salt, to produce an organoclay having the desired rheological properties. The reacted mixture is then filtered to yield a filter cake which comprises an organically modified montmorillonite.
For example, a "wet" processed smectite when reacted with a dimethyl dialkyl ammonium halide, such as dimethyl dihydrogenated tallow ammonium chloride, yields an organoclay which performs well in paints, drilling muds and greases. On the other hand, a "wet" processed smectite when reacted with a dimethyl benzyl alkyl ammonium halide, such as dimethyl benzyl hydrogenated tallow ammonium chloride, yields an organoclay which functions poorly in paints drilling muds and greases, but performs well as a thickener for unsaturated polymers. In the so called "dry" process for preparing organoclays, the step of pretreating the crude clay via water fractionation to isolate the montmorillonite fraction of the crude clay is forsaken. That is, in "dry" process preparation, the crude clay per se is reacted with the quaternary ammonium halide salt rather than merely the montmorillonite fraction of the clay as in "wet" process preparation of the organoclay. Thus, in "dry" process preparation the expense and time consumption associated with water fractionation is avoided and the whole clay, not just the montmorillonite portion thereof, is utilized. Unfortunately, when either of the above-mentioned quaternary ammonium halides was reacted with a bentonite via the so-called "dry" process, the rheological performance of the resulting organoclay was significantly poorer than that of its "wet" process counterpart.